Tafur Bermúdez, Javier

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    Design and development of a 10khz-1mhz ac magnetic susceptomete
    (2011) Tafur Bermúdez, Javier; Juan García, Eduardo J.; College of Engineering; Rinaldi Ramos, Carlos; Rosado, José; Department of Electrical and Computer Engineering; Díaz Rivera, Rubén E.
    Development and improvement of instruments used to characterize magnetic materials is one of the most important tasks in science, which could lead to relevant studies in material science and engineering. The AC magnetic susceptometer is an instrument which consists in a coil arrangement used to investigate magnetic properties such as magnetic susceptibility. Current AC susceptometer design present a limited frequency range, commonly up to 10kHz, preventing the study of magnetic properties dependence on magnetic field frequency, which is crucial in investigations such as specific absorption rate of nanoparticles used for hyperthermia treat- ment. For this reason, the design and development of a frequency improved AC susceptometer operating from 10 kHz to 1MHz with a constant excitation field of approximately 4.25 Oe is of interest. Some considerations such as wire selection to avoid parasitic capacitances between the turns and sensing bridge electronics were further developed in order to extend the operating frequency range. A high speed in- strumentation amplifier with a slew rate over 33V/μs was designed and constructed using voltage feedback LM7171 operational amplifiers. The AC susceptometer operation in the 10 kHz-1MHz frequency range was validated by measuring the complex magnetic susceptibility of cobalt ferrite nanoparticles suspended in different mix- tures of mineral oil and hexane. The viscosity of the solvents were obtained from the Brownian relaxation time equation and compared with the viscosities obtained from a validated instrument. Results were in good agreement with the theoretical Debye model.